Reflecting on Deep Impact

So yesterday, after covering the Deep Impact press conference at JPL and recording for Planetary Radio, my husband and I drove to his parents' house for an Independence Day barbeque. My in-laws asked me about what had been going on this weekend that had kept me working through the holiday. When I explained the nature of the Deep Impact mission my mother-in-law exclaimed, "What! What gives you the right to go around smashing up a comet that was minding its own business?"

I am sure that there are some people reading this who will find her question silly, but I didn't. Behind my mother-in-law's exclamation is a respect and honor for the natural world, rooted deeply in her culture and religion, and a notion that humans should not lightly visit destruction on any part of it. Those are all admirable motives, not to be dismissed. I wish more people had those motives.

What I told my mother-in-law was that, yes, Deep Impact did commit a destructive act. However, although the impact was a violent and energetic one by human standards, it was a weak one by Solar System standards, and, it was not strong enough to affect the course of the comet in any detectable way. Furthermore, I told her, such a mission would not likely have been undertaken on any of the culturally significant, naked-eye comets, like Halley. Tempel 1, though it does have a name, is a tiny comet, one of millions, visible only to select people with strong-enough telescopes. On the other side, the mission provided -- we hope -- a window into the earliest origins of the solar system, and clues to our beginnings.

The analogy I have been using when I talk to people is that the Deep Impact comet crash is very much like a paleoecologist wandering into an ancient forest, selecting one among the many trees in the forest, and using her tiny drill to extract a pencil-wide core from the tree in order to study its rings and understand some things about the history of the Earth's climate. The act is a destructive one -- it drills a hole into a natural object previously undisturbed by humans. But it does not destroy the tree. It does not even significantly impact the health of the tree. Likewise, the Deep Impact mission produced a new hole in a comet in order to see what was inside, but it did not destroy the comet, change its course, or even produce any permanent effect in its outward appearance.

But there is one significant way in which my analogy breaks down. Over the past few decades, tree ring cores have been taken from thousands of trees, producing a huge international database illuminating fine local changes in climate over the past thousands of years. But no one has ever cored a comet before. Tempel 1 was the very first. And that massively increases its cultural significance. Deep Impact possibly gave us the first glimpse humanity has ever had of materials preserved since the very beginnings of our solar system. (I say 'possibly' because after all the science results are not out yet, and the science team has not yet confirmed that they achieved what they hoped for.) Attempting to understand our origins is a powerful motive for study and research, shared across diverse human cultures.

Those of us who were writing about this event for the public tended to focus on the extremes of the event -- the speeds, the power, the technological achievements. In the end, though, the ultimate goals of the mission had to do with understanding our beginnings. I hope that, as the scientific results of the mission come out over the coming weeks and months, the focus will shift from the violence of the event itself to the yield of new understandings of how the Solar System came to be, and what was the nature of the ingredients for the first life on Earth -- the water and organic molecules that were likely contributed to our newborn planet by myriad little comets like Tempel 1.

So, I explained this stuff to my mother-in-law. She thought about it for a minute, then chuckled and said, "All right, I suppose I will let you do this thing!" Which was good, because it had already been done!